Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) that sends data packets to a physical layer transceiver for transmission on the network media.
The Ethernet protocol ISO/IEC 8802-3 (ANSI/IEEE standard 802.3, 1993 edition) defines a half-duplex media access mechanism that permits all stations to access the network channel with equality. The half-duplex mechanism typically operates at either 10 MB/s, or 100 MB/s. A full-duplex environment has also been proposed for Ethernet networks, referred to as IEEE 802.3x, Full-Duplex with Flow Control - Working Draft (0.3). The full-duplex environment provides a two-way, point-to-point communication link between two networks stations using the switched hub, for example at 100 MB/s, so that two stations can simultaneously transmit and receive Ethernet data packets between each other without collision.
The IEEE 802.3z Task Force is currently defining standards for the operation of a shared (i.e., half-duplex) and full-duplex Gigabit Ethernet. The standard will describe a media access control (MAC) layer, a reconciliation layer, a Gigabit-media independent interface (GMII), and physical media dependent sublayers that will implement the physical layer (PHY) of the proposed networks. The proposed networks will enable users to implement Ethernet links capable of operating at a data rate of 1 Gigabit per second in half-duplex mode and 2 Gigabits per second in full-duplex mode.
Currently, the Fast Ethernet standard describes a media independent interface (MII) that is used to connect Fast Ethernet MAC layer devices to the Fast Ethernet devices, enabling users to implement Ethernet links operating at 100 MB/s half-duplex, and 200 MB/s full-duplex.
There currently is no means for users to implement Ethernet links that operate in the range of data rates that exceed 200 MB/s and are lower than 1 Gigabit per second. In addition, efforts at implementing a physical data link at Gigabit transmission rates is very expensive, since the current state of technology does not permit use of copper links for Gigabit data rate transmissions. Hence, only fiber optics can be used to transmit data at Gigabit data rates.